Grain sorghum [Sorghum bicolor (L.) Moench] has been improved by public and private breeding programs utilizing germplasm mostly from within the species.  Different cross-incompatibility mechanisms have prevented its hybridization with species in other sections of the genus.  These incompatibilities have recently been overcome to allow hybridization between S. bicolor (2n = 20) and S. macrospermum (2n = 40), a wild relative in the Chaetosorghum section.  Meiotic chromosome pairing in the interspecific hybrids averaged 3.5 bivalents per pollen mother cell.  Using FISH (Fluorescent In Situ Hybridization), discrimination between chromosomes of the different parents was possible.  It was determined that most bivalents in the hybrids were the result of allosyndetic pairing.  This confirms that chromosomes of the two species are recombining and introgression through genetic recombination is possible.  Previous attempts to backcross the interspecific hybrid as male onto S. bicolor were not successful.  However, the reciprocal cross, using the interspecific hybrid as female, produced immature embryos which were recovered through embryo rescue.  Fifteen BC₁F₁ individuals were produced.  Their chromosome numbers varied from 2n = 36 to 70 and all were male sterile.  Four individuals showed female fertility by producing seed when pollinated by the S. bicolor recurrent parent.  BC₂F₁ individuals (2n = 20) varied in fertility from 0-100% seed set when self pollinated.  These interspecific backcross individuals, with chromosome number equal to the recurrent parent but expressing altered fertility, indicate that introgression from the wild parent likely is occurring and phenotypically affecting the progeny.  Analysis of the amount of DNA introgressed from the S. macrospermum parent into the BC₂F₁ individuals as revealed by AFLP markers is ongoing.  Evaluation of BC₂F₂ individuals for trait variation under field conditions is also under way.  This research demonstrates that S. macrospermum is now available for use in sorghum breeding.